Tractor-semi-trailer combinations are extensively used in the trucking industry to transport goods over the nation's highways. Semi-trailers having a trailer length of 40' are quite common. In addition, proposals have been made to permit the use of trailers even exceeding this length When such long tractor-trailer combinations are used on limited access interstate highways, no particularly significant problems are encountered, since the lanes are wide, and the curves are large radius curves. When the tractor-trailer combination, particularly for such long trailers, is operated on city streets, however, the relatively narrow width of many streets makes it very difficult or impossible to maneuver the tractor-trailer through turns from one street onto a cross do not track the tractor, but tend to be considerably offset, particularly in sharp turns, as the tractor maneuvers through a turn. The result is that trailer lengths considerably shorter than those which are permitted for use in over-highway travel must be employed for inner city travel. As a consequence, transferring of cargo from large trailers to smaller ones for delivery in many areas is necessary, resulting in significantly increased labor costs, as well as the potential for increased loss or damage to the cargos being hauled.
Efforts have been made to provide for controlled or automatic steering of the rear wheels of a tractor-semi-trailer combination to reduce the amount of offset between the rear of the trailer and the tractor during turns, particularly relatively sharp right-angle turns of the type encountered in city streets. One such device is disclosed in the patent to DeWitt. U.S. Pat. No. 4,660,848. The device disclosed in this patent is a telescoping articulating stinger for hauling large shipping containers. When the tractor towing the stinger/trailer encounters sharp turns, an articulated joint operates to steer the rear wheel set to cause the rear of the stinger/trailer to more nearly track the path of the tractor. This device, however, requires clearance for movement of the stinger beneath the container, along with a provision to lock the articulated portion in a straight line when the steering of the rear wheels of the stinger/trailer is not desired.
Another approach to turning the rear wheels of a trailer, in response to the relative movement between the tractor and the trailer at the, fifth wheel connection, is disclosed in the patent to Googe U.S. Pat. No. 2,793,052. The steering mechanism of this patent effectively requires three fifth wheel type of units. A coupling between the fifth wheel linkage of the trailer to the tractor operates a second fifth wheel plate, located rearwardly of the tractor/trailer fifth wheel. Rotational movement of this second fifth wheel mechanism then is applied to additional mechanism for rotating or steering the rear trailer wheels. The multiple fifth wheel mechanisms, used in the device of this patent however, can result in lost motion; and it is possible for the tractor to cut under the device, possibly damaging it. The device of Googe includes an additional provision to permit it to be disconnected for operation of the trailer in a normal fixed-wheel mode.
Another approach for steering the rear wheels of a trailer is disclosed in the patent to Carmody, U.S. Pat. No. 2,286,166. This patent provides a slot at the fifth wheel, which guides a pin attached to one end of an elongated pivoted lever. The lever is pivoted on the trailer at a location spaced from the fifth wheel position toward the trailer. The opposite end of the lever operates a rack and pinion gear to rotate a steering shaft, which is used to effect steering of the rear wheels of the trailer. This is a rather cumbersome apparatus; and because the rack and pinion steering gear must be located beneath the trailer, dirt and debris thrown up from the road by the rear wheels of the tractor, and impacting on the rack and pinion mechanism, can have a highly deleterious effect on its operation.
Three other patents, to Edwards, U.S. Pat. No. 2,359,978; Lorr, U.S. Pat. No. 2,797,106; and Felburn, U.S. Pat. No. 2,959,428, all disclose direct mechanical linkage between a rotating fifth wheel plate and steering apparatus attached to the rear wheels of a trailer. As the amount of relative rotation between the fifth wheel and the front of the trailer is increased, the steering of the rear wheels of the trailer correspondingly is increased.
It is desirable to provide a steering system for the rear wheels of a semi-trailer which is automatic in operation, overcomes the disadvantages of the prior art, is simple to operate, and which automatically limits the amount of pivotal rotation or steering imparted to the rear wheels of the trailer once the relative rotation between the fifth wheel of the tractor and the front of the trailer exceeds a pre-established angular amount.